In recent years, wideband high performance synthesizers have been widely employed in various applications, most of which are implemented with a multi-band VCO to cover a wide frequency range, as shown, for example, generally at 300 in FIG. 3. However, if the frequency range needed to be covered is ultra-wide, a large number of sub-bands is indispensable. Such a large number of sub-bands may cause larger parasitic capacitance, larger VCO tuning gain deviation for different tuning sub-band, a worse mismatch problem, and longer time consumed for a band selection algorithm. The large parasitic capacitance is generally unacceptable in high frequency applications. The mismatch due to complex interconnection degrades the symmetric property of the VCO, which may up-convert much more flicker noise from the bias circuits and the power supply to the output. This is absolutely undesirable, of course. If a smaller number of sub-bands are used, the VCO gain has to be increased to cover the same frequency range. This unavoidable trade-off makes designers frustrated all the time. Thus current techniques present problems.